Purpose: To evaluate the change in the angle of deviation in an incidence cohort of pediatric patients diagnosed with intermittent exotropia during a 20-year period. Design: Retrospective, population-based observational study. Participants: All pediatric (<19 years old) residents of Olmsted County, Minnesota diagnosed with intermittent exotropia (≥10 prism diopters) from January 1, 1975 through December 31, 1994. Methods: The medical records of all potential patients identified by the resources of the Rochester Epidemiology Project were reviewed. Main Outcome Measures: The change in the angle of deviation and its association with treatment were reviewed for each patient. Results: A total of 184 pediatric patients were diagnosed during the study period, of which 138 patients (75.0%) had ≥2 examinations. The deviation resolved in 5 of the 138 patients (3.6%) during a median follow-up of 9.2 years, while the Kaplan-Meier rate of increasing by 10 or more prism diopters (PD) was 23.1% at 5 years and 52.8% at 20 years. The distance deviation increased by a median of 5 PD during the preoperative period in the 55 patients who underwent surgery during a mean follow-up of 3.2 years compared with a zero PD median change in the 83 patients who avoided surgery during a mean follow-up of 7.1 years. The Kaplan-Meier probability of undergoing surgery within 20 years after diagnosis was 74.0% in this population. We were unable to detect a significant association between nonsurgical treatments and a change in the angle of deviation. Conclusions: In this population-based cohort of pediatric patients with intermittent exotropia, the deviation resolved in 4%, and more than half of the patients were expected to have an increase of 10 or more PD within 20 years of their diagnosis. Children who received surgery in this population were significantly more likely to have demonstrated an increase in their deviation during the preoperative period.
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